Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Ecological Species Concept
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Ecological Species Concept
- In responding to selection, populations diverge and play unique roles in the
environment - filling different niches. This ecological specialization will be reflected in
physiological, morphological, or behavioral differences between populations.
Hawaiian Honeycreepers
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Ecological Species Concept
- In responding to selection, populations diverge and play unique roles in the
environment - filling different niches. This ecological specialization will be reflected in
physiological, morphological, or behavioral differences between populations.
- Our classic example of "Character Displacement", where the morphology changes
as a function of the environment - most notably the presence of other species such
as competitors or predators.
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Ecological Species Concept
- In responding to selection, populations diverge and play unique roles in the
environment - filling different niches. This ecological specialization will be reflected in
physiological, morphological, or behavioral differences between populations.
- Our classic example of "Character Displacement", where the morphology changes
as a function of the environment - most notably the presence of other species such
as competitors or predators.
- In the presence of a competitior, G. fortis
uses a different range of seeds and is a
different ecological species than where it
occurs alone. It plays a different role in the
environment and fills a different niche.
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Striking a Balance
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Striking a Balance
- So what preserves the integrity of species - reproductive isolation or ecological
isolation? These are often correlated, so it is tough to tease their independent
contributions apart.
Genetic divergence and
reproductive isolation
Geographic or ecological
isolation
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Striking a Balance
- So what preserves the integrity of species - reproductive isolation or ecological
isolation? These are often correlated, so it is tough to tease their independent
contributions apart.
- Conundrums:
- Selection can produce divergence even when their IS gene flow. (polymorphism)
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Striking a Balance
- So what preserves the integrity of species - reproductive isolation or ecological
isolation? These are often correlated, so it is tough to tease their independent
contributions apart.
- Conundrums:
- Selection can produce divergence even when their IS gene flow. (polymorphism)
- Selection can produce uniformity in absence of gene flow (convergence)
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Striking a Balance
- So what preserves the integrity of species - reproductive isolation or ecological
isolation? These are often correlated, so it is tough to tease their independent
contributions apart.
- Conundrums:
- Selection can produce divergence even when their IS gene flow. (polymorphism)
- Selection can produce uniformity in absence of gene flow (convergence)
- And, gene flow can also keep two populations in different environments similar.
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Striking a Balance
- So what preserves the integrity of species - reproductive isolation or ecological
isolation? These are often correlated, so it is tough to tease their independent
contributions apart.
- Conundrums:
- Selection can produce divergence even when their IS gene flow. (polymorphism)
- Selection can produce uniformity in absence of gene flow (convergence)
- And, gene flow can also keep two populations in different environments similar.
- For bacteria/archaeans, lateral gene transfer (gene flow) creates new species,
with a new unique complement of genes.
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Striking a Balance
- So what preserves the integrity of species - reproductive isolation or ecological
isolation? These are often correlated, so it is tough to tease their independent
contributions apart.
- Conundrums:
- Selection can produce divergence even when their IS gene flow. (polymorphism)
- Selection can produce uniformity in absence of gene flow (convergence)
- And, gene flow can also keep two populations in different environments similar.
- For bacteria/archaeans, lateral gene transfer (gene flow) creates new species,
with a new unique complement of genes.
- Need to appreciate that the relative importance of different factors may vary
depending on the organism - does it have high dispersal and isolation probability?
Can it change rapidly? These things will vary with the type of organisms (large
mammals vs. insects).
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
- correlated phenotypic characters. Quantitative characteristics can have bimodal
distributions. However, it is unusual for a single species to be bimodal for lots of
characters.
Wing Pattern
Wing Shape
H. erato
H. melpomene
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
- correlated phenotypic characters. Quantitative characteristics can have bimodal
distributions. However, it is unusual for a single species to be bimodal for lots of
characters.
Body Size
H. erato
H. melpomene
Wing Shape
- If you observe this (big ones are red, with wispy
antenna, small wings and fast flight; small ones are
blue with short antenna, large wings and slow
flight), then you probably have two reproductively
isolated groups.
H. melpomene
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
- correlated phenotypic characters. Quantitative characteristics can have bimodal
distributions. However, it is unusual for a single species to be bimodal for lots of
characters.
- If you observe this (big ones are red, with wispy antenna, small wings and fast
flight; small ones are blue with short antenna, large wings and slow flight), then you
probably have two reproductively isolated groups.
- may miss morphologically similar sibling species, or lump polymorphic species.
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
- correlated phenotypic characters. Quantitative characteristics can have bimodal
distributions. However, it is unusual for a single species to be bimodal for lots of
characters.
- If you observe this (big ones are red, with wispy antenna, small wings and fast
flight; small ones are blue with short antenna, large wings and slow flight), then you
probably have two reproductively isolated groups.
- may miss morphologically similar sibling species, or lump polymorphic species.
- want to focus on traits of little selective value, or copulatory organs
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
- Genetic Distance - distance correlates with divergence that can occur both before
and after reproductive isolation. So, there is a fairly continuous function of declining
similarity as reproductive isolation develops, dependent on average size of the
populations. Within a group, often we see 'species' associated with a particular
amount of genetic distance.
A summary of hybridization experiments involving 119 pairs of closely related
Drosophila species.
Prezygotic Isolation: Mate Selection:
I = 1 - ( number of heterospecific matings) / (number of homospecific matings)
Post-zygotic Isolation: avg: Offspring inviable or sterile (1) or viable and fertile (0)
Coyne and Orr. 1989. Patterns of speciation in
Drosophila. Evolution 43: 362-381.
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
- Genetic Distance
- Compute Nei's Genetic distance:
D = -ln [ ∑pi1pi2/ √ ∑pi12 ∑ pi22]
- So, for Population 1 and 2:
- ∑pi1pi2 = (0.7*0.2) + (0.3*0.8) = 0.38
- denominator = √ (.49+.09) * (.04+.64) = 0.628
D12 = -ln (0.38/0.62) = 0.50
- calculate these values FOR EACH locus, and
then average the I's or D's together to get the final Genetic
Distance. The more loci, the better.
p1 = 0.7
q1 = 0.3
p2 = 0.2
q2 = 0.8
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
- Genetic Distance - distance correlates with divergence that can occur both before
and after reproductive isolation. So, there is a fairly continuous function of declining
similarity as reproductive isolation develops, dependent on average size of the
populations. Within a group, often we see 'species' associated with a particular
amount of genetic distance.
- Compute Nei's Genetic Distance
- CAVEATS:
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
- Genetic Distance - distance correlates with divergence that can occur both before
and after reproductive isolation. So, there is a fairly continuous function of declining
similarity as reproductive isolation develops, dependent on average size of the
populations. Within a group, often we see 'species' associated with a particular
amount of genetic distance.
- Compute Nei's Genetic Distance
- CAVEATS:
- Genetic diffs do not necessarily correlate with morphological diffs; small
genetic diffs can mean large morphological change (developmental genes), or large
genetic differences can be hidden by morphological similarity (norms of reaction).
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
- Genetic Distance - distance correlates with divergence that can occur both before
and after reproductive isolation. So, there is a fairly continuous function of declining
similarity as reproductive isolation develops, dependent on average size of the
populations. Within a group, often we see 'species' associated with a particular
amount of genetic distance.
- Compute Nei's Genetic Distance
- CAVEATS:
- Genetic diffs do not necessarily correlate with morphological diffs; small
genetic diffs can mean large morphological change (developmental genes), or large
genetic change can be hidden by morphological similarity (norms of reaction).
- Still, genetic similarity is a more direct measure of degree of isolation.
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
- Genetic Distance - distance correlates with divergence that can occur both before
and after reproductive isolation. So, there is a fairly continuous function of declining
similarity as reproductive isolation develops, dependent on average size of the
populations. Within a group, often we see 'species' associated with a particular
amount of genetic distance.
- Compute Nei's Genetic Distance
- CAVEATS:
- Genetic diffs do not necessarily correlate with morphological diffs; small
genetic diffs can mean large morphological change (developmental genes), or large
genetic change can be hidden by morphological similarity (norms of reaction).
- Still, genetic similarity is a more direct measure of degree of isolation.
- Also, there is no suggestion that divergence in these loci CAUSE
speciation. Rather, these loci are simply used as 'markers' or indicators of general
genetic distance.
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
C. Hybrid Analyses
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
C. Hybrid Analyses
- Create hybrids and examine their fertility. Infertility may be due to:
- Epistatic interactions between loci derived from different parents. Maybe
species one has A1A1B1B1 and species 2 has A2A2B2B2, and maybe A1 and B1
don't work together. If one is a sex linked gene, then sterility might be sex-specific.
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
C. Hybrid Analyses
- Create hybrids and examine their fertility. Infertility may be due to:
- Epistatic interactions between loci derived from different parents. Maybe
species one has A1A1B1B1 and species 2 has A2A2B2B2, and maybe A1 and B1
don't work together. If one is a sex linked gene, then sterility might be sex-specific.
- Hybrids that receive different inversion chromosomes may have lower
fitness because crossing over produces aneuploid gametes - with chromosomes that
lack centromeres and are lost from the cell line.
Inversion (changes the order of genes on a chromosome)
The only functional
gametes are those that
DID NOT cross over –
and preserve the
parental combination of
alleles
Inversions in different populations of D. pseudoobscura
(Dobzhansky& Sturtevant 1938)
Relative frequencies (percentages)
of five chromosomal inversions in D.
pseudoobscura in different
geographic regions.
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
C. Hybrid Analyses
- Create hybrids and examine their fertility. Infertility may be due to:
- Epistatic interactions between loci derived from different parents. Maybe
species one has A1A1B1B1 and species 2 has A2A2B2B2, and maybe A1 and B1
don't work together. If one is a sex linked gene, then sterility might be sex-specific.
- Hybrids that receive different inversion chromosomes may have lower
fitness because crossing over produces aneuploid gametes - with chromosomes that
lack centromeres and are lost from the cell line.
- Hybrids receiving chromosomes from parents with different reciprocal
translocations may not have neat homologous sets.
Species and Speciation
I. Species Concepts
II. Recognizing Species
III. Making Species - Reproductive Isolation
Species and Speciation
I. Species Concepts
II. Recognizing Species
III. Making Species - Reproductive Isolation
A. Pre-Zygotic Barriers
Species and Speciation
I. Species Concepts
II. Recognizing Species
III. Making Species - Reproductive Isolation
A. Pre-Zygotic Barriers
1. Geographic Isolation (large scale or habitat)
Drosophila speciation on the Hawaiian Islands.
Obbard D J et al. Mol Biol Evol 2012;29:3459-3473
© The Author 2012. Published by Oxford University Press on behalf of the Society for Molecular
Biology and Evolution.
Species and Speciation
I. Species Concepts
II. Recognizing Species
III. Making Species - Reproductive Isolation
A. Pre-Zygotic Barriers
1. Geographic Isolation (large scale or habitat)
2. Temporal Isolation
Species and Speciation
I. Species Concepts
II. Recognizing Species
III. Making Species - Reproductive Isolation
A. Pre-Zygotic Barriers
1. Geographic Isolation (large scale or habitat)
2. Temporal Isolation
3. Behavior Isolation - don't recognize one another as mates
Western Meadowlark
Eastern Meadowlark
Species and Speciation
I. Species Concepts
II. Recognizing Species
III. Making Species - Reproductive Isolation
A. Pre-Zygotic Barriers
1. Geographic Isolation (large scale or habitat)
2. Temporal Isolation
3. Behavior Isolation - don't recognize one another as mates
4. Mechanical isolation - genitalia don't fit; limit pollinators
Species and Speciation
I. Species Concepts
II. Recognizing Species
III. Making Species - Reproductive Isolation
A. Pre-Zygotic Barriers
1. Geographic Isolation (large scale or habitat)
2. Temporal Isolation
3. Behavior Isolation - don't recognize one another as mates
4. Mechanical isolation - genitalia don't fit
5. Gametic Isolation - gametes transfered but sperm can't fertilize egg; this
is a common isolation mechanism in species that spawn at the same time
Species and Speciation
I. Species Concepts
II. Recognizing Species
III. Making Species - Reproductive Isolation
A. Pre-Zygotic Barriers
1. Geographic Isolation (large scale or habitat)
2. Temporal Isolation
3. Behavior Isolation - don't recognize one another as mates
4. Mechanical isolation - genitalia don't fit
5. Gametic Isolation - gametes transfered but sperm can't fertilize egg
B. Post-Zygotic Isolation
Species and Speciation
I. Species Concepts
II. Recognizing Species
III. Making Species - Reproductive Isolation
A. Pre-Zygotic Barriers
1. Geographic Isolation (large scale or habitat)
2. Temporal Isolation
3. Behavior Isolation - don't recognize one another as mates
4. Mechanical isolation - genitalia don't fit
5. Gametic Isolation - gametes transfered but sperm can't fertilize egg
B. Post-Zygotic Isolation
1. Genomic Incompatibility - zygote dies
Species and Speciation
I. Species Concepts
II. Recognizing Species
III. Making Species - Reproductive Isolation
A. Pre-Zygotic Barriers
1. Geographic Isolation (large scale or habitat)
2. Temporal Isolation
3. Behavior Isolation - don't recognize one another as mates
4. Mechanical isolation - genitalia don't fit
5. Gametic Isolation - gametes transfered but sperm can't fertilize egg
B. Post-Zygotic Isolation
1. Genomic Incompatibility - zygote dies
2. Hybrid Inviability - F1 has lower survival
Crazy hybrids
Species and Speciation
I. Species Concepts
II. Recognizing Species
III. Making Species - Reproductive Isolation
A. Pre-Zygotic Barriers
1. Geographic Isolation (large scale or habitat)
2. Temporal Isolation
3. Behavior Isolation - don't recognize one another as mates
4. Mechanical isolation - genitalia don't fit
5. Gametic Isolation - gametes transfered but sperm can't fertilize egg
B. Post-Zygotic Isolation
1. Genomic Incompatibility - zygote dies
2. Hybrid Inviability - F1 has lower survival
3. Hybrid Sterility - F1 has reduced reproductive success
Horse: 64 chromosomes
Donkey: 62 chromosomes
Mule: 63 chromosomes
Species and Speciation
I. Species Concepts
II. Recognizing Species
III. Making Species - Reproductive Isolation
A. Pre-Zygotic Barriers
1. Geographic Isolation (large scale or habitat)
2. Temporal Isolation
3. Behavior Isolation - don't recognize one another as mates
4. Mechanical isolation - genitalia don't fit
5. Gametic Isolation - gametes transfered but sperm can't fertilize egg
B. Post-Zygotic Isolation
1. Genomic Incompatibility - zygote dies
2. Hybrid Inviability - F1 has lower survival
3. Hybrid Sterility - F1 has reduced reproductive success
4. F2 breakdown - F1's survive but F2's have incompatible combo's of genes
AABB
x
aabb
F1: AaBb = ok
F2:
A-B- = ok
A-bb = no
aaB- = no
aabb = ok
Species and Speciation
I. Species Concepts
II. Recognizing Species
III. Making Species - Reproductive Isolation
IV. Speciation